A buffer, by definition, is a solution that resist change in pH. In a buffered solution, adding acid will only result in a small decrease in pH whereas adding the same volume and concentration of acid to a non-buffered solution will cause a much larger change in pH.

Each element in a chemical equation has an oxidation state, and you will have to assign these oxidation states to each element in order to determine the correct redox reaction stoichiometry. These states can be fairly easily determined just by looking at the periodic table.

First of all, we need to know the Rate Determining Step (RDS) to write the rate law. Note that this is the slow step, as the part of the overall mechanism that proceeds the slowest will ultimately determine the overall rate of the reaction.